Dear,

As per JEE rules Foreign Nationals who are planning to apply for IIT also have to take the same test as Indian citizens, the JEE Advanced. Hence it makes it easier for PIO and OCI holders to apply for JEE Advanced and go through the same procedure as Indian citizens.

You have to apply for JEE Main and mention whether you are PIO or OCI in the online application. You will fall under General Category and will be ranked along with Indian citizens. If shortlisted and opted you can go for admission to IIT in par with the General category Indian citizens

On the day of admission you will be asked to get a letter from Parents / Guardians to be their point of contact and Supporters of your education. Fees for IIT differ for Foreign Nationals but definitely less than Private Engineering colleges normal Fees. (Few IITs ask for Foreign Nationals, fee few don't).

Hope this helps!